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BQ24032A Vout with USB input power

Nathan Kro
Intellectual 270 points
Other Parts Discussed in Thread: BQ24032A, BQ24030, BQ24038

I was looking for a battery charger that would handle both a DC charger and a USB charger at the same time.  The charger needs to be a power path implementation.  I had chosen the BQ24032A as it seemed to fit my needs, but I now noticed that the Vout voltage is only regulated to 4.4V when the DC charger is present and the active source.  The datasheet seems to indicate that if USB is the input charging source, Vout is just Vusb minus the drop out voltage, so effectively 5V; "Note that the OUT pin regulates at 4.4V ±0.1V, with an adaptor input, on the bq24032A/bq24038 ICs, is switched straight through on the bq24030/5 ICs (up to 6V); and, on USB inputs (all ICs) is switched straight through from the USB input to the OUT pin."

This won't work for my system as the input needs to be 4.5V or less.  Can you please confirm that I am reading the datasheet correctly that the "regulated 4.4V output" is really only regulated for DC inputs?  It seems odd that the part would regulate down to 4.4V for the DC input but not for the USB input.

Thanks

  • 0
    TI__Guru 56650 points

    The output should always try to regulate ouput at 4.4V.

    "If the system and battery load is less than the selected regulated limit, then Q3 is fully on and VOUT is approximately (V(USB)-V(USB-DO)).  "

    But, if (V(USB)-V(USB-DO))>4.4V, the output should be regulated to 4.4V.

  • 0 in reply to Wang5577
    Intellectual 270 points

    Wang

    Thanks for the response.  In reading the few sentences before that statement, it leads me to think the "regulated limit" being discussed is the current limit, not the voltage limit; can you please confirm this?  Text below:

    "In this case, the system load is powered directly from the USB port through the internal switch Q3 (see
    Figure 14). Note in this case, Q3 regulates the total current to the 100 mA or 500 mA level, as selected on the
    ISET2 input. Switch Q1 is turned off in this mode. If the system and battery load is less than the selected
    regulated limit, then Q3 is fully on and VOUT is approximately (V(USB)-V(USB-DO))."

    Nate

  • 0 in reply to Nathan Kro
    TI__Guru 56650 points

    On the page 4th of datasheet, bq24032A ouput is regulated at 4.4V.

  • 0 in reply to Wang5577
    Intellectual 270 points

    I see now that Note 4 on page 4 answers my question, "(4) When power is applied to the USB pin and PSEL is low, the USB input is switched straight through to the OUT pin (not regulated). This
    voltage may drop to the DPPM-OUT threshold or battery voltage (which ever is higher) if the USB input current limit is active."

    So the USB input is NOT regulated to 4.4V.

  • 0 in reply to Nathan Kro
    TI__Guru 56650 points

    Yes. That note 4 gives the description about output voltage when power is applied to the USB pin and PSEL is low.